The most important features of the human sense of hearing are those that promote the segregation and integration of acoustic features in a way that results in the determination of actual sound sources. Since environments often include multiple and simultaneous objects, the auditory system must function fundamentally as a "separation machine" whose job it is to determine individual sources from the complex mixture of source sounds reaching the ears. This sort of auditory scene analysis is now well appreciated as an important function of human hearing. We suggest here that these functions are also primitive features of a general vertebrate sense of hearing, and that these are the functions that have defined success and fitness most importantly throughout the evolution of the vertebrate auditory system. The overall goals are to determine how these primitive functions of the vertebrate sense of hearing operate in a relatively simple vertebrate species. One goal is to help establish a biological and evolutionary context within which human hearing can be more fully understood. Aim 1: We will investigate the capacities of a simple vertebrate species to determine source characteristics when there are multiple, simultaneous sound sources present (i.e., auditory scene analysis and source segregation). We will investigate other acoustic features that promote auditory perceptual segregation in human listeners for their effects on fish listeners. These features include onset asynchrony, amplitude modulation, duration, harmonic structure, (and spatial origin: Aim 2). These features will be investigated for their effects on perception using behavioral conditioning methods using stimulus generalization paradigms. Aim 2: We will investigate auditory source segregation using multiple, discrete local sources. We will analyze the effects of the spatial origin of sources independently of the non-spatial acoustic features (Aim 1) that may play a role in sound source sesegregation. Aim 3: We will determine the nature of the neural codes and representations underlying source segregation by recording from peripheral and central auditory neurons in response to the same signals and sources used in the above behavioral experiments. We will focus on understanding the dimensions of neural activity that the brain could use in segregating and integrating simultaneous acoustic components from one or more sources. [unreadable] [unreadable]